Abstract : P50CdC37 is a recently discovered gene which functions in the establishment of protein kinase signaling pathways by functioning in complex with molecular chaperone Hsp9O. The proposed mode of function of Cdc37/Hsp9O complex is that Cdc37 targets intrinsically unstable kinases to the complex with Hsp9O, and this transient interaction of newly synthesized kinases with the complex is necessary for their stabilization and/or folding and further activation. Through stabilization of key kinases, Cdc37 expression may be a pre-requisite for activation of the signaling pathways and, as a result, for proliferatiQn. CdC37 expression may be required for proliferative aspects of development and Cdc37 would be required for cell proliferation induced by oncogenes that utilize protein kinase signaling pathways in which Cdc37 participates. To test this hypothesis, we created and analyzed a transgenic mouse model where Cdc37 expression is driven by MMTV promoter, directing the expression into breast epithelial cells, salivary and lacrimal gland. The effects of Cdc37 overexpression in mammary and salivary glands are generally consistent with CdC37 having a positive effect on proliferation and reveal a novel collaboration with the c-myc oncogene in cellular transformation.